The present invention relates to video tape recorders. More particularly, the present invention relates to improved slip ring and brush assemblies for transmitting electrical signals and power across a rotating interface in a video tape recorder.
Video tape recorders employ rotating record/reproduce head assemblies. In such recorders, tape which is used as the recording medium is wrapped partially around a drum having a rotating record/reproduce head assembly. In general, the head assembly is connected to a rotatable spindle inside the drum. During the data recording or reproducing process, the tape is moved (or held stationary) while the recording or reproducing is accomplished, i.e., as the recording/reproducing head(s) rotates with the spindle. By way of example, representative video tape recorders utilizing record/reproduce head assemblies may include models DVW, DNW, HDW Series manufactured by Sony Corporation.
In such video tape recorders, electrical signals, as well as electrical power signals, must be transmitted to and from the rotating head assembly. Accordingly, slip ring and brush assemblies have been introduced and employed to various degrees to carry electrical signals between the rotating heads and other equipment with which the rotating head has relative motion. Slip ring and brush assemblies are typically used in electromechanical systems that require unrestrained, continuous rotation while transmitting power and/or electrical signals from a stationary conductor to a rotating structure. In general, slip ring assemblies include a rotor, which is a rotating part, and a stator, which is a stationary part about which the rotor turns. Brush assemblies typically include a brush holder and a brush, both of which are stationary. More particularly, the rotor generally comprises a rotating conductive ring, which is contacted by a non-rotating conductive brush.
To facilitate discussion, FIGS. 1A-1C illustrate an exemplary prior art slip ring and brush system 10 used in video recording devices. FIG. 1A is a side elevation view, in cross section, of the system 10, FIG. 1B is a cut away top view of the system 10, and FIG. 1C is a bottom view of the system 10. As shown, the slip ring assembly 10 includes a rotor 12 and a stator 14. The rotor 12 includes a base 16 and a shaft 18. The base 16 is configured for mating with a drum assembly of the video recorder (not shown) and the shaft 18 is configured for carrying a plurality of slip rings 20. As shown in FIG. 1A, the bottom of the base 16 includes a protrusion 22, which physically engages a spindle of the drum assembly. The bottom of the base 16 also includes mounting posts 24, which couple the system 10 to the spindle (e.g., with machine screws). Still further, the bottom of the base 16 includes a bottom surface 26 having a plurality of contact pads 28 disposed thereon (shown in FIG. 1C). The contact pads 28 are separately and electrically connected to the slip rings 20 carried by the shaft 18. The contact pads 28 are for engaging contact pins that are electrically coupled to a head assembly disposed inside the drum assembly.
With regard to the stator 14, the stator 14 includes a support member 30 that is rotatably mounted onto the shaft 18 with a first set of bearings 32 positioned at an upper portion of the shaft 18, and a second set of bearings 34 positioned at a lower portion of the shaft 18. As shown, the slip rings 20 are disposed between each of the set of bearings 32, 34. The stator 14 also includes a first brush assembly 36 positioned to a first side of the shaft 18, and a second brush assembly 38 positioned to a second side of the shaft 18. The second side is opposite the first side. Both of the brush assemblies 36, 38 are mounted to the support member 30 and each brush assembly includes a brush holder 39 and a plurality of single filament brushes 40 for electrically contacting the slip rings 20. Furthermore, each of the single filament brushes 40 is coupled to a transport ribbon cable 42, which is arranged for carrying electrical signals and/or power to and from an external device such as a printed circuit board. Moreover, a rectangular cover 44 is typically disposed over the stator/rotor combination.
Unfortunately, the design and implementation of the above assembly leads to problems which may shorten part life and the proper functioning of the video recording device in which it is used. One problem associated with the above assembly is that excessive vibrations may be encountered during rotation of the rotor about the stator. Excessive vibrations may be formed by an improperly mated or misaligned connection (e.g., un-balanced) at the rotor/spindle interface. For example, if the protrusion is too small then the rotor may wobble during rotation. Excessive vibrations tend to cause increased bearing wear, and may even cause the bearings to stiffen or seize Stiffened bearings may impede the rotation of the rotor or may induce more vibration. Excessive vibrations may also reduce contact between the brushes and the slip rings. Furthermore, the type of ball bearings used and the placement of the ball bearings on the rotating shaft may exacerbate the vibration problem.
Another problem with the above assembly 10 is that each of the brushes 40 is a monolithic or mono-filament member having a rectangular or cylindrical cross-section. Although the surface of the brush 40 is in contact with the rotating slip ring 20, irregularities in the ring surface and uneven wear properties of the brush limit contact between the brush 40 and the ring 20 to only a few discrete points. These discrete points of contact between the brush 40 and the slip ring 20 cause the brush biasing force to be concentrated on these few points. This concentration of force results in localized high pressures on these few points and this leads to unexpected wear of both the brush and ring surface. Furthermore, the resultant wear debris may increase electrical resistance to the flow path of electricity through the assembly or may contaminate portions of the video recorder, for example, the head assembly found beneath the assembly.
Other problems associated with the above slip ring and brush assembly include a double brush assembly, which increases complexity and costs, a slip ring assembly that is not fully enclosed (e.g., open space 46) and therefore may lead to contamination of both the assembly 10 and any components found beneath the assembly 10 (e.g., video recorder), and contact pads 28 that are thinly plated and thus may easily wear. By way of example, the contact pads 28 are typically formed from gold plated copper elements.
Thus, there is a need for improved slip assemblies for transmitting electrical signals and power across a rotating interface in a video tape recorder.
The invention relates, in one embodiment, to a slip ring assembly for use in a video recording device. The slip ring assembly includes a base for coupling with a rotatable spindle located in a drum assembly of a video tape recorder. The base includes a plurality of electrically conductive contact pads for electrically engaging a plurality of electrically conductive leads disposed on the rotatable spindle and electrically coupled to a record/reproduce head assembly. The slip ring assembly further includes a shaft having a first portion coupled to the base and a second portion extending longitudinally from the first portion. The slip ring assembly additionally includes a plurality of electrically conductive slip rings positioned on the second portion of the shaft, where each slip ring is separated by an insulating medium and electrically coupled to an individual one of the plurality of contact pads. The slip ring assembly also includes a pedestal rotatably supported on the first portion of the shaft.
In some embodiments, a brush assembly for transmitting electrical energy between a plurality of stationary conductors and the plurality of slip rings is provided. The brush assembly includes a plurality of fiber brushes for electrically contacting individual ones of the plurality of slip rings. Each of the fiber brushes includes a plurality of fibers that are maintained in a bundle.
The invention relates, in another embodiment, to a slip ring and brush assembly for transmitting electrical energy between a stationary conductor and a rotating head assembly of a video recording device. The slip ring and brush assembly includes a rotor having a base and a shaft. The base is arranged to couple with a rotatable spindle located in a drum assembly of a video tape recorder. The base includes a conductive contact pad for electrically engaging a plurality of electrically conductive leads disposed on the rotatable spindle and electrically coupled to the rotating head assembly. The shaft extends from the base and includes an electrically conductive slip ring positioned on the shaft. The electrically conductive slip ring is electrically coupled to the electrically conductive contact pad. The slip ring and brush assembly further includes a stator that is rotatably coupled to the rotor. The stator includes a pedestal and a sheath. The slip ring and brush assembly also includes a brush holder, which is mounted to the pedestal. The brush holder is configured to hold a fiber brush in biased contact with the slip ring. The fiber brush is electrically coupled to the stationary conductor, and includes a plurality of electrically conductive fibers that are grouped together to form a single fiber brush.